Optically pumped, surface-emitting semiconductor laser device and method for the manufacture thereof

ABSTRACT

The invention is directed to an optically pumped surface-emitting semiconductor laser device having at least one radiation-generating quantum well structure and at least one pump radiation source for optically pumping the quantum well structure, whereby the pump radiation source comprises an edge-emitting semiconductor structure. The radiation-generating quantum well structure and the edge-emitting semiconductor structure are epitaxially grown on a common substrate. A very efficient and uniform optical pumping of the radiation-generating quantum well structure is advantageously possible with this monolithically produced semiconductor laser device. Methods for manufacturing inventive semiconductor laser devices are also specified.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention is directed to an optically pumped surface-emittingsemiconductor laser device having at least one radiation-generatingquantum well structure and at least one pump radiation source foroptically pumping the quantum well structure, whereby the pump radiationsource comprises an edge-emitting semiconductor structure.

[0003] 2. Description of the Related Art

[0004] A semiconductor laser device of the species initially describedis disclosed by U.S. Pat. No. 5,991,318. An optically pumped verticalresonator semiconductor laser having a monolithic surface-emittingsemiconductor layer structure is disclosed therein. Given this knowndevice, the optical pump radiation, whose wavelength is shorter thanthat of the generated laser emission, is supplied by an edge-emittingsemiconductor laser diode. The edge-emitting semiconductor laser diodeis externally arranged such that the pump radiation is beamed obliquelyin from the front into the intensification region of thesurface-emitting semiconductor layer structure.

[0005] A particular problem given this known device is comprise thereinthat the pump laser must be exactly positioned relative to thesurface-emitting semiconductor layer structure and, additionally,requires an optical means for beam focusing in order to image the pumpradiation exactly into the desired region of the surface-emittingsemiconductor layer structure. These measures involve considerabletechnological outlay.

[0006] In addition to the losses at the optics, moreover, couplinglosses also occur that reduce the overall efficiency of the system.

[0007] Another problem is comprised therein that only a few quantumwells can be excited by pump radiation due to the pumping from thefront.

SUMMARY OF THE INVENTION

[0008] The object of the present invention is comprised in makingavailable a semiconductor laser device of the species initially citedwith simplified adjustment of pump source and surface-emitting layerstructure and with high output power. Further, a technically simplemethod for manufacturing such a device is recited.

[0009] According to the invention, the radiation-generating quantum wellstructure and the edge-emitting semiconductor structure are epitaxiallygrown on a common substrate given an optically pumped surface-emittingsemiconductor laser device of the species initially cited. The layerthicknesses of the individual semiconductor layers can be very exactlyset in the epitaxy, so that a high positioning precision of theedge-emitting semiconductor structure relative to theradiation-generating quantum well structure is advantageously achieved.

[0010] With the inventive device, further, a uniform optical pumping ofthe quantum well structure can be achieved for high output powers in thefundamental mode.

[0011] In an advantageous embodiment, the surface-emitting quantum wellstructure and the pump radiation source are arranged side-by-side on thesubstrate such that a radiation-emitting region of the pump radiationsource and the quantum well structure lie at the same height above thesubstrate. What is thereby achieved is that pump radiation is laterallycoupled into the quantum well structure during operation of thesemiconductor laser device. This means that the beam axis of the pumpradiation proceeds essentially parallel to the substrate surface and,thus, essentially vertically relative to the beam axis of the laser beamgenerated by the surface-emitting semiconductor laser device.

[0012] Given such a device, the quantum well structure is “pumped”transparently at first from the lateral surfaces during operation until,finally, the entire lateral cross-sectional area thereof is laseractive. Due to the lateral optical pumping, moreover, a uniform fillingof the quantum wells with charge carriers is achieved.

[0013] Preferably, the quantum well structure is surrounded by theedge-emitting semiconductor structure. At least one gain-guidedradiation-emitting active region that serves as pump radiation source isformed therein on the basis of at least one current injection path onthe surface of the semiconductor laser structure. Alternatively, atleast one index-guided radiation-emitting active region of theedge-emitting semiconductor structure serves as pump radiation source.This is defined, for example, with at least one current injection pathon the surface of the edge-emitting semiconductor structure incombination with, for example, etched trenches in the semiconductorstructure fashioned along the current injection path.

[0014] Preferably, the ends of the current injection path facing towardthe radiation-generating quantum well structure have a spacing of 10μthrough 50 μm, especially preferred approximately 30 μm. As a resultthereof, disturbing leakage currents and other disturbing influences atthe boundary surfaces between the edge-emitting semiconductor structureand the surface-emitting layer sequence, i.e. the input surfaces for thepump radiation, are reduced.

[0015] The aforementioned embodiments can be advantageously fabricatedoverall with traditional semiconductor process technology.

[0016] When, during operation of the device, an adequately high currentflows through the injection paths into the active layer of the pumpradiation source, an intensified spontaneous emission (super-radiation)is formed, this being guided into the surface-emitting laser region andbeing absorbed thereat. The electron-hole pairs generated as a resultthereof are collected in the quantum well and lead to the inversion inthe intensification region of the surface-emitting laser structure.

[0017] The excitation of the surface-emitting laser structure can ensueby pumping the quantum well structure or confinement layers adjacentthereto. When pumping the confinement layers, the pump efficiency ispreferably enhanced in that the band gap thereof decreases toward thequantum well structure. This, for example, can be achieved by modifyingthe material composition. As a result thereof, internally electricalfields are generated in the confinement layers that drive the opticallygenerated charge carriers into the active quantum well region.

[0018] In an especially preferred embodiment, a plurality of pumpradiation sources are arranged star-like around the quantum wellstructure, so that the quantum well structure is transparently “pumped”and laser-active over its entire lateral cross-section in a short timeand very uniformly.

[0019] The boundary surface between edge-emitting semiconductorstructure ad quantum well structure is preferably at least partiallyreflective. What is thereby achieved is that a back-reflection into theedge-emitting semiconductor structure derives at the edge to thesurface-emitting laser region, this leading to the formation of laserradiation in the pump source and, thus, to enhanced pump efficiency.

[0020] Generating laser radiation as pump radiation and, thus, enhancedpump efficiency is alternatively achieved in that respectively two pumpradiation sources arranged at opposite sides of the quantum wellstructure together form a laser structure. The end faces of theedge-emitting radiation sources lying parallel to one another and facingaway from the quantum well structure are fashioned as mirror surfacesfor this purpose and serve as a resonator mirror. These, for example,can be generated by cleaving and/or etching (for example, dry etching)and can be provided with a passivation layer and/or can be highlyreflectively mirrored.

[0021] The opposite pump radiation sources are coupled during operationvia the transparently pumped quantum well structure to form a single,coherently resonating laser. Given optimum end mirroring, the entireoptical power stored in the pump laser is then available as pump powerexcept for the losses at the boundary surfaces between pump laser andsurface-emitting laser.

[0022] Preferably, the edge-emitting semiconductor structure comprises alarge optical cavity (LOC) structure. Given this, an active layer isembedded between a first to the second waveguide layer that are in turnembedded between a first and a second cladding layer.

[0023] In an advantageous development of the invention, it is providedthat the edge-emitting semiconductor structure be fashioned as ringlaser. What is thereby to be understood by a ring laser is a laserstructure wherein ring modes can form during operation. The design ofthe appertaining laser resonator in ring form is thereby advantageous,as to be explained below, but not compulsory.

[0024] The resonator of such a ring laser can be formed with totallyreflective boundary surfaces, so that no highly reflective mirrors areadvantageously required. The risk of a lower radiation yield due todamage at the mirrors is thus also reduced. Further, a ring laser isdistinguished by an advantageously large mode volume and by a high modestability.

[0025] Preferably, the quantum well structure to be pumped is arrangedwithin the ring resonator, so that the entire resonator-internalradiation field is available for pumping the quantum well structure. Itis thereby especially advantageous to arrange the active layer of theedge-emitting semiconductor structure and the quantum well structure atthe same height above the substrate, so that a large overlap derivesbetween the volume of the quantum well structure to be pumped and theradiation field of the edge-emitting semiconductor structure and, thus,a high pump efficiency derives.

[0026] In an advantageous development of the invention, the resonator ofthe ring laser is formed by an annularly closed waveguide. The guidanceof the pump radiation field therein ensues by total reflection at thelimitations of the waveguide, so that highly reflective mirrors are alsoadvantageously not required here. Further, the pump radiation field canbe very well-adapted to the volume of the quantum well structure to bepumped as a result of the shaping of the annularly closed waveguide.

[0027] The etch-emitting semiconductor structure in a preferreddevelopment of the invention is surrounded by a medium whose refractiveindex is lower than the refractive index of the semiconductor structure.As a result thereof, a totally reflective surface that serves aslimitation of the laser resonator arises at the transition from thesemiconductor into the optically thinner, surrounding medium. Forforming an annularly closed waveguide, a recess filled with theoptically thinner medium can be arranged within the edge-emittingsemiconductor structure.

[0028] Due to the low refractive index, air or some other gaseous mediumis particularly suitable as surrounding medium. Alternatively, theedge-emitting semiconductor structure can also be surrounded by someother materials such as, for example, a semiconductor material, asemiconductor oxide or a dielectric having a lower refractive index.

[0029] Preferably, the semiconductor structure is formed as acylindrical stack of circular or annular semiconductor layers. Thecylindrical semiconductor body shaped in this way simultaneouslyrepresents the ring laser resonator at whose cladding surfaces theradiant field is guided in totally reflecting fashion.

[0030] Alternatively, the semiconductor structure can also be formedprismatically as a stack of semiconductor layers in the form of polygonsor polygonal rings. As a result of this shaping, a largely uniform beamdistribution and, correspondingly, a largely homogeneous pump densitycan be achieved in the quantum pot structure.

[0031] A stack of semiconductor layers of the described shape can beformed comparatively simply, for example by etching from a previouslyepitaxially produced semiconductor layer sequence. Advantageously, thelaser resonator of the edge-emitting semiconductor structure issimultaneously also formed with the shaping of the semiconductor bodywithout additional mirrorings being required.

[0032] In an especially preferred development of the semiconductordevice, the quantum well structure has more than ten quantum wells. Thishigh number of quantum wells is possible because all quantum wells aredirectly pumped as a result of the lateral input of the pump radiation.As a result thereof, a high gain in the surface-emitting quantum wellstructure is advantageously achieved.

[0033] The edge-emitting semiconductor structure is preferably fashionedsuch that it generates a pump wave whose maximum lies at the height ofthe quantum wells above the substrate, especially preferably at thelevel of the center of the quantum well structure.

[0034] In order to obtain especially high output powers, theedge-emitting semiconductor structure in an advantageous development isfashioned as what is referred to as a multiple stack or micro-stackedlaser having a plurality of laser-active layer sequences (for example,double heterostructures) that are connected in series via tunneltransitions. The quantum well structure then advantageously comprises aplurality of quantum well groups that respectively lie at the height ofa laser-active layer sequence of the pump source.

[0035] In a preferred method for manufacturing an optically pumped,surface-emitting semiconductor laser device according to theaforementioned embodiments, a first semiconductor layer sequencesuitable for a surface-emitting semiconductor laser and having at leastone quantum well structure is initially applied onto a substrate.Subsequently, the first semiconductor layer sequence is removed outsidethe intended laser region. An edge-emitting, second semiconductor layersequence is deposited subsequently on the region over the substrate thatwas uncovered after the removal of the first semiconductor layersequence, said second semiconductor layer sequence being suitable forgenerating pump radiation and transmitting it into the quantum wellstructure. Subsequently, at least one current injection path isfashioned in the edge-emitting semiconductor layer sequence.

[0036] Preferably, a buffer layer is first applied onto the substrate. Afirst confinement layer is deposited thereon. A quantum well structuresuitable for a surface-emitting semiconductor laser is subsequentlyapplied onto the first confinement layer and this quantum well structureis followed by a second confinement layer. After the removal of theconfinement layers and of the quantum well structure and, partially, ofthe buffer layer outside the intended surface-emitting laser region, afirst cladding layer, a first waveguide layer, an active layer, a secondwaveguide layer and a second cladding layer are successively appliedonto the region of the buffer layer that is then uncovered. Therespective layer thicknesses are designed such that the pump radiationgenerated in the active layer proceeds into the quantum well structure.

[0037] In another embodiment of the semiconductor laser device accordingto the invention, the radiation-emitting quantum well structure and thepump radiation source are arranged above one another on the substrate.The quantum well structure is thereby optically coupled to theedge-emitting semiconductor structure, so that pump radiation from thepump radiation source is guided into the quantum well structure duringoperation of the semiconductor laser device.

[0038] The edge-emitting semiconductor structure preferably comprises afirst waveguide layer and—as viewed from the substrate—a secondwaveguide layer following thereupon between which an active layer isarranged. The quantum well structure is epitaxially grown on the secondwaveguide layer, covers only a sub-region of the edge-emittingsemiconductor structure and is optically coupled thereto.

[0039] For improving the infeed of the pump radiation into the quantumwell structure, the boundary surface between second waveguide layer andadjacent cladding layer is bent or buckled toward the quantum wellstructure in the proximity of the surface-emitting laser region.

[0040] In order to improve the infeed of the pump radiation into thesurface-emitting semiconductor structure, the refractive index of thesecond waveguide layer is advantageously higher than the refractiveindex of the first waveguide layer and/or the active layer is placedsymmetrical in the waveguide fashioned by the two waveguide layers.

[0041] Analogous to the above-described, first embodiment, one or moregain-guided and/or index-guide, radiation-emitting active regions arefashioned as pump radiation sources in the edge-emitting semiconductorstructure.

[0042] In a preferred method for manufacturing an optically pumped,surface-emitting semiconductor laser device according to theaforementioned, second basic embodiment and the developments thereof, anedge-emitting semiconductor laser layer sequence is first applied onto asubstrate. A surface-emitting semiconductor laser layer sequence havingat least one quantum well structure is then applied thereon.Subsequently, the surface-emitting semiconductor laser layer sequence isremoved outside the intended laser region before at least one currentinjection path is fashioned in the edge-emitting semiconductor layersequence.

[0043] To this end, a buffer layer is preferably first applied onto thesubstrate. Subsequently, a first waveguide layer, an active layer and asecond waveguide layer are deposited successively thereon. A firstconfinement layer, a surface-emitting semiconductor laser layer sequencehaving a quantum well structure and a second confinement layer areapplied onto the edge-emitting layer sequence produced in this way. Theconfinement layers, the surface-emitting semiconductor laser layersequence and, in part, the second waveguide layer are then removedoutside the intended surface-emitting laser region.

[0044] In an inventive method for manufacturing an optically pumped,surface-emitting semiconductor laser device having a ring laser as pumpradiation source, a surface-emitting semiconductor layer sequence havingat least one quantum well structure—as already set forth—as already setforth—is initially applied on a substrate, the layer sequence is removedoutside the planned laser region, and the edge-emitting semiconductorstructure of the pump radiation source is applied onto the regionuncovered as a result thereof.

[0045] Subsequently, the outside region of the edge-emittingsemiconductor structure is removed for shaping the laser resonator. Acentral sub-region in the inside of the semiconductor structure isthereby also preferably eroded for forming a ring resonator. The removalof the sub-regions can, for example, ensue with a dry etching process.Advantageously, a complicated post-processing of the etched surfaces isnot required.

[0046] Alternatively, the method steps can also be applied in adifferent sequence. For example, an edge-emitting semiconductorstructure can be applied first on the substrate, this then being erodedin the planned laser region of the quantum well structure (which is yetto be formed). In the next step, the surface-emitting semiconductorlayer sequence having at least one quantum well structure is applied onthe uncovered region. Subsequently, the outside region of theedge-emitting semiconductor structure is again removed for shaping thelaser resonator. In a modification of the method, the shaping of thelaser resonator can also occur before the application of thesurface-emitting semiconductor layer sequence.

[0047] In a preferred development of the two above-recited embodiments,a highly reflective Bragg reflector layer sequence is fashioned at oneside of the quantum well structure, this representing a resonator mirrorof the surface-emitting laser structure. A further Bragg reflector layersequence or an external mirror is arranged at the opposite side of thequantum well structure as second, partially transmissive resonatormirror.

[0048] Preferably, the substrate is composed of a material that istransmissive for the laser beam generated in the semiconductor laserdevice, and the highly reflective Bragg reflector is arranged at thatside of the quantum well structure facing away from the substrate. Thisenables a short connection between the semiconductor structures and aheat sink and, thus, a good heat elimination from the semiconductorstructures.

[0049] In order to prevent disturbing transverse modes (modes parallelto the substrate—whispering modes), absorber layers are arranged in theedge region is and/or in etching structures of the surface-emittingsemiconductor laser layer sequence.

[0050] The inventive semiconductor laser device is particularly suitablefor employment in an external resonator wherein a frequency-selectedelement and/or a frequency doubler is located.

[0051] Advantageously, the inventive semiconductor laser device—viamodulation of the pump laser—can be modulated by modulation of the pumpcurrent or via a short-circuit connection of the surface-emittingsemiconductor laser layer sequence.

[0052] Further advantageous developments and improvements of the deviceand of the method of the invention derive from the exemplary embodimentsdescribed below in conjunction with FIGS. 1 through 14.

DESCRIPTION OF THE DRAWINGS

[0053]FIG. 1 shows a schematic illustration of a section through a firstexemplary embodiment.

[0054]FIGS. 2a through 2 e show a schematic illustration of a methodsequence for manufacturing the exemplary embodiment according to FIG. 1.

[0055]FIG. 3a shows a schematic illustration of a section through asecond exemplary embodiment.

[0056]FIG. 3b shows a schematic illustration of an advantageousdevelopment of the waveguide of the exemplary embodiment according toFIG. 3a.

[0057]FIGS. 4a through 4 c show a schematic illustration of a methodsequence for manufacturing the exemplary embodiment according to FIG. 3.

[0058]FIG. 5 shows a schematic illustration of a plan view onto a firstarrangement of current injection paths on an edge-emitting semiconductorstructure.

[0059]FIG. 6 shows a schematic illustration of a plan view onto a secondarrangement of current injection paths on an edge-emitting semiconductorstructure.

[0060]FIG. 7 shows a schematic illustration of a plan view onto a thirdarrangement of current injection paths on an edge-emitting semiconductorstructure.

[0061]FIGS. 8a and 8 b show a schematic illustrations of semiconductorlaser devices with absorber layer.

[0062]FIGS. 9a and 9 b show a schematic illustration of a section and ofa plan view of a first exemplary embodiment having a ring laser as pumpradiation source.

[0063]FIG. 10 shows a schematic illustration of a plan view of a secondexemplary embodiment having a ring laser as pump radiation source.

[0064]FIGS. 11a and 11 b show a schematic illustration of a plan view ofa third and fourth exemplary embodiment having respectively two ringlasers as pump radiation source.

[0065]FIGS. 12 and 12b show a schematic illustration of a methodsequence for manufacturing the exemplary embodiment according to FIG. 9.

[0066]FIG. 13 shows a schematic illustration of an inventivesemiconductor laser device having an external resonator.

[0067]FIG. 14 shows a schematic illustration of a modulatablesemiconductor laser device of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] Identical elements or elements having the same effect areprovided with the same reference characters in the Figures.

[0069] The exemplary embodiment of FIG. 1 is, for example, an opticallypumped surface-emitting semiconductor laser chip having a laser emissionat 1030 nm. Therein, a buffer layer 6 is applied on a substrate 1. Thesubstrate 6 is composed, for example, of GaAs and the buffer layer 6 iscomposed of undoped GaAs.

[0070] A surface-emitting semiconductor laser structure 10 having aquantum well structure 11 is applied on the buffer layer 6 centrallyover the substrate, this representing the surface-emitting laser region15. The semiconductor laser structure 10 is composed of a firstconfinement layer 12 located directly on the buffer layer 6, of aquantum well structure 11 arranged on said confinement layer 12 and of asecond confinement layer 13 applied on the quantum well structure 11.

[0071] The confinement layers 12, 13 are composed, for example, ofundoped GaAs, and the quantum well structure 11 comprises, for example,a plurality (≧3) of quantum wells that are composed of undoped InGaAswhose thickness is set to the emission at 1030 nm and between whichbarrier layers of GaAs are located.

[0072] A Bragg mirror 3 having, for example, 28 through 30 periodsGaAlAs (10% Al)/GaAlAs (90% Al) that represents a highly reflectiveresonator mirror is deposited over the surface-emitting semiconductorlaser structure.

[0073] An edge-emitting semiconductor laser structure 21, for example aknow large optical cavity (LOC) single quantum well (SQW) laserstructure for an emission at approximately 1 μm, is deposited in theenvironment of the laser region 15 on the buffer layer 6. This structure21 is composed, for example, of a first cladding layer 28 (for example,n-GaAl_(0.65)As), of a first waveguide layer 23 (for example,n-GaAl_(0.1)As), of an active layer 25 (for example, an undopedInGaAs-SQW), of a second waveguide layer 24 (for example,p-GaAl_(0.1)As) and of a second cladding layer 29 (for example,p-GaAl_(0.65)As).

[0074] For example, a p⁺-doped GaAs layer can be applied on the secondcladding layer 29 as cover layer 30.

[0075] The LOC region 22 is arranged at the same height as the quantumwell region of the surface-emitting laser structure 10; preferably, theactive layer 25 is located at the same height above the substrate 1 asthe quantum well structure 11.

[0076] In a particular embodiment of the exemplary embodiment, theedge-emitting semiconductor structure 21 comprises a plurality of activelayers 25 that are connected in series via tunnel transitions. Analogousthereto, the quantum well structure 11 comprises a plurality of quantumwell groups that respectively lie at the height of an active layer 25 ofthe edge-emitting semiconductor structure 21.

[0077] All semiconductor layers are, for example, produced withmetallorganic vapor phase epitaxy (MOVPE).

[0078] In the mirrors 31 proceeding perpendicular to the layers of theedge-emitting semiconductor laser structure 21 are located in theproximity of the outer edge of the edge-emitting semiconductor laserstructure 21, these end mirrors 31 extending at least into the firstcladding layer 28, here up to the buffer layer 6, proceeding from thecover layer 30. For example, these are produced after the growth of theedge-emitting semiconductor laser structure 21 by etching (for example,reactive ion etching) of corresponding trenches and the subsequentfilling thereof with highly reflective material. Respectively twomirrors 31 parallel to one another are arranged at opposite sides of thequantum well structure 11 (see FIGS. 5 and 6).

[0079] Alternatively, the end mirrors can be manufactured in a known wayby cleaving the way for along crystal planes. As shown in FIG. 1, theseare then not necessarily arranged in the chip but are formed by thecloven chip lateral surfaces (see FIG. 7).

[0080] In electrically insulating mask layer 7, for example a siliconnitride, an aluminum oxide or a silicon oxide layer, with which currentinjection paths 26 of the edge-emitting semiconductor laser structure 21are defined are located on the free surface of the cover layer 30 and ofthe Bragg mirror 3 (see FIGS. 5 and 6. A p-contact layer 32, for examplea known contact metallization, is applied on the mask layer 7 and—in therecesses thereof for the current injection paths 26—on the cover layer30.

[0081] For example, six stripe arrays having 15 stripes (4 μm stripe,10μpitch) with approximately 150 μm active width that are arrangedsymmetrically start-shaped around the surface-emitting laser region 15are selected for the pump source.

[0082] Preferably, the ends of the current injection paths 26 facingtoward the radiation-generating quantum well structure 11 have a spacingof 10 μm through 50 μm, particularly preferably of approximately 30 μm,therefrom. As a result thereof, disturbing leakage currents and otherdisturbing influences at the boundary surfaces between the edge-emittingsemiconductor structure 21 and the surface-emitting layer sequence 10are reduced, i.e. at the infeed surfaces for the pump radiation 2.

[0083] All current injection paths 26 can be provided with a commonp-contact layer 32, as a result whereof the radiation-emitting regionsof the edge-emitting structure are connected parallel to one another inoperation. Given an intended, separate drive of these individualradiation-emitting regions, a correspondingly structured p-conductive,first contact layer 32 is applied. As a result thereof, an optimizedpump light distribution (for example, similar to a Gauss profile) can beproduced over the lateral cross-section of the surface-emittingstructure.

[0084] For generating index-guided pump regions in the edge-emittingstructure 21, trenches manufactured, for example, by etching can beformed therein along the current injection paths 26 (said trenches notbeing shown in the Figures), these extending, for example, up to 0.5 μminto the second waveguide layer 24. As a result thereof, an improvedwave guidance is achieved at the edges of the pump regions.

[0085] The principal surface 16 of the substrate 1 facing away from thesemiconductor structure is provided with an n-conductive, second contactlayer 9, for example likewise a known contact metallization, except foran exit window 8 for the laser beam (indicated with the arrow 5).

[0086] The principal surface 16 of the substrate is preferablyanti-bloomed in the region of the exit window 8 in order to reduceback-reflections into the chip.

[0087] A laser resonator of the surface-emitting laser structure 10 canbe fashioned as a Bragg mirror 3 and an external, further mirror (notshown in FIG. 1) arranged at the opposite side of the substrate 1 or canbe formed of a further Bragg mirror arranged between the substrate 1 andthe quantum well structure 11.

[0088] During operation of the semiconductor chip, pump radiation(indicated by the arrows 2) is generated in a region of theedge-emitting semiconductor structure 21 that represents the pumpradiation source 20 and that are defined by the current injection paths26, and this pump radiation is coupled into the quantum well structure11 of the surface-emitting laser structure 10.

[0089] Given adequate back-reflection at the boundary surface betweenedge-emitting structure 21 and surface-emitting structure 10 and asuitable position of the end mirrors 31, laser radiation that leads toan enhanced pump efficiency is generated in the edge-emitting structure21.

[0090] Preferably, the end mirrors 31 are arranged such relative to oneanother that these form a laser resonator for two radiation-emittingregions of the edge-emitting structure 21 that lie opposite one another.The two radiation-emitting regions lying opposite one another are thencoupled to form a single coherently resonating laser after thetransparent pumping of the surface-emitting laser structure 10. Givenoptimum mirroring of the end mirrors 31, the entire optical powergenerated by the pump laser is available as pump power except for lossesat the boundary surface between edge-emitting structure 21 andsurface-emitting structure 10.

[0091] Given the method schematically shown in FIGS. 2a through 2 e formanufacturing the exemplary embodiment according to FIG. 1, the bufferlayer 6, the first confinement layer 12, the quantum well structure 11,the second confinement layer 13 and the Bragg mirror layers 3 areinitially successively applied onto the substrate 1, for example byMOVPE (FIG. 2a).

[0092] Subsequently, an etching mask 17 (for example, a Si-nitridemask), is applied onto the region of this layer sequence provided assurface-emitting laser region 15. Subsequently, the Bragg mirror layers3, the confinement layers 12 and 13, the quantum well structure 11 and,in part, the buffer layer 6 are removed, for example by etching, forexample dry-etching with Cl chemistry, outside the intendedsurface-emitting laser region 15 (FIG. 2b). The first cladding layer 28,the first waveguide layer 23, the active layer 25, the second waveguidelayer 24, the second cladding layer 29 and the cover layer 30 aresuccessively applied then on the uncovered region of the buffer layer 6,for example again with MOVPE (FIG. 2c).

[0093] With, for example, reactive ion etching and suitably known masktechnology, trenches for the end mirrors 31 are then etched (see FIG.2d) in the most recently applied edge-emitting structure 21, thesetrenches being subsequently coated or filled with reflection-enhancingmaterial. The etching mask 17 is also removed.

[0094] Subsequently, the electrically insulating mask layer 7 is appliedonto the cover layer 30 and onto the Bragg mirror 3 before the p-contactlayer 32 and the n-contact layer 9 are finally produced (FIG. 2e).

[0095] Before the application of the insulating mask layer 7, thetrenches described above in conjunction with FIG. 1 are optionallyproduced for generating index-guided pump lasers, being produced byetching.

[0096] In order to reduce radiation losses, the substrate 1 ispreferably thinned to less than 100 μm or completely removed after theMOVPE.

[0097] In the exemplary embodiment according to FIG. 3, a buffer layer 6is initially situated surface-wide on the substrate 1 and anedge-emitting semiconductor laser structure 21 is arranged thereonsurface-wide wherein an active layer 25 is arranged between a firstwaveguide layer 23 and a second waveguide layer 24.

[0098] In a planned laser region 15 over the middle of the substrate 1,a surface-emitting quantum well structure 11 is grown on the secondwaveguide layer 24 followed by a confinement layer 13 and a Bragg mirrorlayer sequence 3.

[0099] An electrically insulating mask layer 7 that comprises recessesfor current injection paths 26 of the edge-emitting structure 21 (seeFIG. 7) is applied in the region around the laser region 15 onto thesecond waveguide layer 24 or, potentially, onto a highly doped coverlayer applied thereon. A first contact layer 32 is located on theelectrically insulating mask layer 7 and in the recesses thereof on thesecond semiconductor layer or, on the cover layer and a second contactlayer 9 having an exit window for the laser beam (indicated with thearrow 5) is arranged at that side of the substrate 1 lying thereopposite.

[0100] For producing index-guided pump regions in the edge-emittingstructure 21, trenches manufactured, for example, by etching can befashioned (not shown in the Figures) in the second waveguide layer 24along the current injection paths 26. An improved waveguidance at theedges of the pump regions is achieved as a result thereof.

[0101] Cloven sidewalls of the chip, for example, are provided here asend mirrors 31 of the edge-emitting structure 21.

[0102] During operation, pump laser radiation is generated in theedge-emitting laser structure, a part thereof being coupled into thequantum well structure 11 lying thereabove.

[0103] In order to promote the infeed, the active layer 25 isasymmetrically located in the waveguide formed by the two waveguidelayers 23, 24. Alternatively or additionally, the refractive index ofthe second waveguide layer 24 can be higher than that of the firstwaveguide layer 23 and/or the second waveguide layer can be pulled uptoward the laser region 15 in the direction of the quantum wellstructure 11 for the same purpose (See FIG. 3b).

[0104] The materials recited for the corresponding layers of theexemplary embodiment according to FIG. 1 can be used by way of examplehere as materials for the various layers.

[0105] A laser resonator of the surface-emitting laser structure 10 canalso be formed in this exemplary embodiment from the Bragg mirror 3 andfrom an external, further mirror (not shown in FIG. 3a) arranged at theopposite side of the substrate 1 or a further Bragg mirror arrangedbetween the substrate 1 and the quantum well structure 11.

[0106] Given the method for manufacturing a device according to theexemplary embodiment of FIG. 3a that is schematically shown in FIGS. 4athrough 4 c, a buffer layer 6 is first applied onto the substrate 1. Thefirst waveguide layer 23, the active layer 25 and the second waveguidelayer 24 are subsequently successively grown thereon. Subsequently, thequantum well structure 11 is grown onto the second waveguide layer 24,followed by the confinement layer 13 and the Bragg mirror layer 3 (FIG.4a). These layers are produced, for example, with MOVPE.

[0107] Subsequently, an etching mask 17 is applied onto the sub-regionof the layer sequence that has been grown and that is provided as laserregion 15, and the Bragg mirror layer 3, the confinement layer 13, thequantum well structure 11 and, in part, the second waveguide layer 24are removed outside the laser region 15 with etching (FIG. 4b).

[0108] Subsequently and for definition of the current injection paths26, the electrically insulating mask layer 7 is applied onto the secondwaveguide layer 24 before the contact layer 32 is then deposited.

[0109] Subsequently, the second contact layer 9 having an exit window 8is applied onto the principal surface of the substrate 1 lying oppositethe semiconductor layer sequence (FIG. 4c).

[0110] In order to reduce radiation losses, the substrate 1 here is alsopreferably thinned too, for example, less then 100 μm or is completelyremoved following the MOVPE.

[0111] The inventive, so-called wafer lasers are preferably solderedwith the Bragg mirror down onto a heat sink. One electrode is located onthe heat sink and the second is generated by bonding on the wafer lasersurface.

[0112] In order to prevent disturbing transverse modes (modes parallelto the substrate—whispering modes), absorber layers 18 (see FIGS. 8a and8 b) are arranged in the edge region and/or in etched structures of thesurface-emitting semiconductor laser layer sequence 15. Suitableabsorber materials for such applications are known and are therefore notexplained in greater detail here.

[0113]FIG. 9a shows a section through an exemplary embodiment of anoptically pumped, surface-emitting semiconductor device having a ringlaser as pump radiation source. The sequence of the individualsemiconductor layers essentially corresponds to the exemplary embodimentshown in FIG. 1.

[0114] Differing from the semiconductor device shown in FIG. 1, theedge-emitting semiconductor structure 21, comprising the first claddinglayer 28 (for example, n-GaAl_(0.65)As), the first waveguide layer 23(for example, n-GaAl_(0.1)As), the active layer 25 (for example,InGaAs-SQW), the second waveguide layer 24 (for example, p-GaAl_(0.1)As)and the second cladding layer 29 (for example, p-GaAl_(0.65)As), as aring laser.

[0115] The plan view onto the semiconductor body shown in FIG. 9billustrates this. The sectional view according to FIG. 9a corresponds toa vertical section along line A-A.

[0116] In the plan view, the edge-emitting semiconductor structure 21comprises an octagonal shape having four full rotational symmetry aswell as a quadratic, central recess 38. The quantum well structure to bepumped and circular in the plan view is completely arranged within theoctagonal ring formed in this way. This octagonal ring forms a ringresonator in the form of a totally reflective, closed waveguide.

[0117] During operation, cyclically circulating ring modes resonate inthis waveguide, illustrated, for example, with reference to the modes 37a, b, c, these optically pumping the quantum well structure 11. As aresult of the total reflection at the outside surfaces, the outputlosses in this exemplary embodiment are extremely low, so that theentire resonator-internal radiation field is advantageously availablefor pumping the quantum well structure 11.

[0118] As a result of the illustrated shaping of the octagonal ring, thering modes 37 a, 37 b and 37 c are essentially of the same priority andpropagate uniformly. A largely uniform radiation field thus derives inradial direction (along the line B-B) and, correspondingly, a largelyuniform pump density derives in the quantum well structure 11 to bepumped.

[0119] The second mirror required for a laser mode of thesurface-emitting semiconductor laser structure 10 is not integrated inthe semiconductor body in the illustrated exemplary embodiment but isprovided as external mirror (also see FIG. 13). Alternatively, thissecond mirror can also be fashioned in the semiconductor body in a way(not shown) similar to the mirror 3. In this case, the second mirrorwould have to be arranged, for example, within the provided laser region15 between the buffer layer 6 and the quantum well structure 11.

[0120]FIG. 10 shows another exemplary embodiment of an inventivesemiconductor laser device in plan view. Differing from the exemplaryembodiment described above, the totally reflective waveguide isfashioned as a circular ring here. The quantum well structure 11 to bepumped is completely arranged within the ring region.

[0121] A plurality of ring modes can resonate within the annularresonator. The illustrated mode 39 merely indicates one possibleexample. The quantum well structure 11, additionally, is pumped by aplurality of further modes with high efficiency.

[0122] As derives from FIG. 10, the central recess 38 can also beforegone for simplification, so that the resonator comprises a solidcircular area as cross-section. As a result thereof, the manufacturingoutlay is advantageously reduced. However, modes that proceed throughthe resonator center can then resonate up to a certain extent. Thesemodes are not totally reflected at the resonator limitation andtherefore have comparatively high output losses that ultimately reducethe pump efficiency.

[0123]FIG. 11a shows a further exemplary embodiment of the inventionwherein the quantum well structure 11 is pumped by two ring lasers thatare independent of one another. These are fundamentally constructed likethe ring laser of the first exemplary embodiment.

[0124] The appertaining waveguides 44, 45 cross in two regions 46 a, b,whereby the quantum well structure 11 to be pumped is arranged in theregion 46 a. To pump density in the quantum well structure 11 isenhanced further with this arrangement having two ring lasers. Theessential pump modes are again shown by way of example with reference tothe modes 37 a, b, c, d, e, f. Advantageously, a largely uniform pumpdensity again derives here as in the case of the first exemplaryembodiment.

[0125]FIG. 11b shows an advantageous version of the arrangement shown inFIG. 3a that is particularly distinguished in that the shaping of thecrossing, annular waveguides 44 and 45 is simplified. To that end, thecross-sections of the central recesses 40 and 41 are reduced totriangles. The lateral recesses 43 shown in FIG. 11a and the centralrecess 42 are foregone. The manufacturing outlay is advantageouslyreduced as a result of this simplification without significantlydeteriorating the laser function.

[0126] As indicated in FIG. 11b, a second quantum well structure 47could, further, also be fashioned in the second crossing region 46 b ofthe two ring lasers.

[0127]FIG. 12 schematically shows two method steps for manufacturing aninventive semiconductor laser device.

[0128] As already described and shown in FIGS. 2a, 2 b and 2 c, themethod begins with the application of the buffer layer 6, of the firstconfinement layer 12, of the quantum well structure 11, of the secondconfinement layer 13 and of the Bragg mirror layers 3 on a substrate 1,for example with MOVPE. Subsequently, an etching mask 7 is applied ontothe region of this layer sequence provided as surface-emitting laserregion 15, and the stack of Bragg mirror layers 3, confinement layers 12and 13, quantum well structure 11 and parts of the buffer layer 6outside the intended surface-laser region 15 are removed. The firstcladding layer 28, the firs waveguide layer 23, the active layer 25, thesecond waveguide layer 24, the second cladding layer 29 and the coverlayer 30 are successively applied onto the uncovered region of thebuffer layer 6, for example again with MOVPE (not shown, see FIGS. 2a,b, c).

[0129] According to FIG. 12a, subsequently, the outside regions and thecentral region of the semiconductor structure are eroded for forming thetotally reflective, closed waveguide. This, for example, can ensue withreactive ion etching upon employment of a suitable, known masktechnique.

[0130] The lateral surfaces of the edge-emitting semiconductor structuremanufactured in this way require no optical coating and forming nearlyloss-free ring laser resonator.

[0131] Finally, the etching mask 17 is removed, the electricallyinsulating mask layer 7 is applied onto the Bragg mirror 11 and thesurface is covered with a p-contact layer 32. The substrate is providedwith n-contact surfaces 9 (FIG. 12b).

[0132] The inventive semiconductor laser devices particularly suited foremployment in an external resonator with an external mirror 33 and apartially transmissive concave reflection mirror 34 in which afrequency-selected element 35 and/or a frequency doubler 36 is located(see FIG. 13).

[0133] Advantageously, the inventive semiconductor laser device can thenbe modulated via modulation of the pump source (by modulating the pumpcurrent) or via a short-circuit connection of the surface-emittingsemiconductor laser layer sequence (FIG. 14).

[0134] The above-described structures can be employed not only in theInGaAlAs employed by way of example but, for example, can also beemployed in the InGaN, InGaAsP or in the InGaAIP system.

[0135] Given a wafer laser in the InGaN system for an emission at 470nm, the quantum wells are composed, for example InGaN for 450 nmemission, the confinement layers are composed of InGaN with reducedrefractive index, and the Bragg mirrors are composed of an InGaAlNsystem. The pump laser structure comprises an active region with quantumwells of InGaN for emission at approximately 400 nm as well as waveguidelayers and cladding layers of GaAlN, wherein the desired refractiveindices are set by variation of the Al content.

[0136] Although other modifications and changes may be suggested bythose skilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

We claim:
 1. An optically pumped surface-emitting semiconductor laserdevice comprising: a radiation-generating quantum well structure formedby a semi-conductor layer sequence, said semi-conductor layer sequencebeing expitaxially and successively grown on a common substrate; and apump radiation source with a radiation region for optically pumping theradiation generating quantum well structure, said pump radiation sourceincluding an edge-emitting semiconductor structure, said edge-emittingsemiconductor structure being formed by the semi-conductor layersequence being expitaxially and successively grown on the commonsubstrate.
 2. An optically pumped surface-emitting semiconductor laserdevice according to claim 1, wherein the radiation generating quantumwell structure and the pump radiation source are being arrangedside-by-side such that: the radiation-generating quantum well structureand the radiation-emitting region of the pump radiation source lie at asame height above the common substrate; and a pump radiation from thepump radiation source is being laterally coupled into the radiationgenerating quantum well structure during operation of the opticallypumped surface emitting semiconductor laser device.
 3. An opticallypumped surface-emitting semiconductor laser device according to claim 2,wherein: the radiation-generating quantum well structure is beingsurrounded by the edge-emitting semiconductor structure; and the pumpradiation source is a gain-guided radiation-emitting active region beingformed on a basis of a current injection path on a surface of theedge-emitting semiconductor laser structure.
 4. An optically pumpedsurface-emitting semiconductor laser device according to claim 2,wherein: the radiation-generating quantum well structure is beingsurrounded by the edge-emitting semiconductor structure; and the pumpradiation source is an index-guided radiation-emitting active regionthat is being defined on a basis of a current injection path on asurface of the edge emitting semiconductor structure in combination withtrenches in the edge-emitting semiconductor structure formed along acurrent injection path.
 5. An optically pumped surface-emittingsemiconductor laser device according to claim 4 , wherein ends ofcurrent injection paths facing toward the radiation-generating quantumwell structure include a spacing of 10 μm-50 μm therefrom.
 6. Anoptically pumped surface-emitting semiconductor laser device accordingto claim 1, wherein the pump radiation source includes two pumpradiation sources being arranged at opposite sides of the radiationgenerating quantum well structure, said two pump radiation sources foremitting pump radiation into the radiation generating quantum wellstructure during operation.
 7. An optically pumped surface-emittingsemiconductor laser device according to claim 1, wherein the pumpradiation source includes a plurality of pump radiation sources beingarranged in a star-like manner around the radiation generating quantumwell structure, said plurality of pump radiation sources for emittingpump radiation into the radiation generating quantum well structureduring operation.
 8. An optically pumped surface-emitting semiconductorlaser device according to claim 6, wherein the two pump radiationsources together form a laser structure for an optical pumping withlaser emission.
 9. An optically pumped surface-emitting semiconductorlaser device according to claim 1, wherein the pump radiation sourceinclude a ring laser.
 10. An optically pumped surface-emittingsemiconductor laser device according to claim 9, wherein the radiationgenerating quantum well structure is arranged within a resonator of thering laser.
 11. An optically pumped surface-emitting semiconductor laserdevice according to 10, wherein the resonator of the ring laser isformed by an annularly closed waveguide.
 12. An optically pumpedsurface-emitting semiconductor laser device according to claim 9,wherein the edge-emitting semiconductor structure is being surrounded bya medium with a refractive index being less than a refractive index ofthe edge-emitting semiconductor structure.
 13. An optically pumpedsurface-emitting Semiconductor laser device according to claim 9,wherein the edge-emitting semiconductor structure is surrounded by atleast one of a gaseous medium and a dielectric.
 14. An optically pumpedsurface-emitting semiconductor laser device according to claim 9,wherein the edge-emitting semiconductor structure is being formed as acylindrical body with one of a circular and annular cross section. 15.An optically pumped surface-emitting Semiconductor laser deviceaccording to claim 9, wherein the edge-emitting semiconductor structureis being formed as a prismatic body with a cross section in a form ofone of a polygon and a polygonal ring.
 16. An optically pumpedsurface-emitting semiconductor laser device according to claim 1,wherein the edge-emitting semiconductor structure includes an activelayer embedded between a first waveguide layer and a second waveguidelayer, said first wave guide layer and said second waveguide layer beingembedded between a first cladding layer and a second cladding layer. 17.An optically pumped surface-emitting semiconductor laser deviceaccording to claim 16, wherein: a boundary surface between theedge-emitting semiconductor structure and the radiation generatingquantum well structure is partially reflective.
 18. An optically pumpedsurface-emitting semiconductor laser device according to claim 1,wherein: the edge-emitting semiconductor structure includes a pluralityof active layers that are being connected in series with tunneltransitions, and the radiation-generating quantum well structureincludes a plurality of quantum well groups that respectively lie at asame height above the common substrate as an active layer of theedge-emitting semiconductor structure.
 19. An optically pumpedsurface-emitting semiconductor laser device according to claim 1,wherein: the radiation-emitting quantum well structure and the pumpradiation source are arranged above one another on the common substrate;and the radiation-emitting quantum well structure is being opticallycoupled to the edge-emitting semiconductor structure, so that a pumpradiation is being guided into the radiation-emitting quantum wellstructure during operation of the optically pumped surface emittingsemiconductor laser device.
 20. An optically pumped surface-emittingsemiconductor laser device according to claim 19, wherein: theedge-emitting semiconductor structure includes a first waveguide layerand a second waveguide layer and an active layer, said active layerarranged between the first waveguide layer and the second waveguidelayer; and, the quantum well structure being epitaxially grown on thesecond waveguide layer, covers only a sub-region of the edge-emittingsemiconductor structure and is being optically coupled thereto, so thata part of the pump radiation generated in the edge-emittingsemiconductor structure is being guided into the quantum well structure.21. An optically pumped surface-emitting semiconductor laser deviceaccording to claim 20, wherein: the pump radiation source is again-guided radiation-emitting active region being formed in theedge-emitting semiconductor structure via a correspondingly structuredcurrent injection path on a surface of the second waveguide layer. 22.An optically pumped surface-emitting Semiconductor laser deviceaccording to claim 21, wherein: the pump radiation source is beingformed in combination with correspondingly etched trenches in the secondwaveguide layer.
 23. An optically pumped surface-emitting Semiconductorlaser device according to claim 20, wherein a refractive index of thesecond waveguide layer is higher than a refractive index of the firstwaveguide layer.
 24. An optically pumped surface-emitting semiconductorlaser device according to claim 20, wherein the active layer is beingasymmetrically placed in the waveguide formed by the first waveguidelayer and the second waveguide layer.
 25. An optically pumpedsurface-emitting semiconductor laser device according to claim 2,wherein: the common substrate is being composed of a material beingtransmissive for a laser beam generated in the optically pumped surfaceemitting semiconductor laser device; and a resonator mirror layer withan optimally substantially high reflection coefficient is being appliedon a side of the radiation generating quantum well structure facing awayfrom the common substrate.
 26. A method for manufacturing an opticallypumped surface-emitting semiconductor laser device comprising: applyinga surface-emitting semiconductor laser layer sequence onto a commonsubstrate, said surface-emitting semiconductor layer sequence having aquantum well structure; removing the surface-emitting semiconductorlaser layer sequence outside an intended laser region and exposing anexposed region; applying an edge-emitting semiconductor layer sequenceonto the exposed region over the common substrate, said exposed regionbeing exposed via said removing step, said exposed region being suitablefor transmitting pump radiation into the quantum well structure; andforming a current injection path in the edge-emitting semiconductorlayer sequence.
 27. A method for manufacturing an optically pumpedsurface-emitting according to claim 26, wherein: the step for applyingthe surface-emitting semiconductor laser layer sequence furthercomprises the steps of: applying a buffer layer onto the commonsubstrate; applying a first confinement layer onto the buffer layer;applying the quantum well structure suited for a surface-emittingsemiconductor laser onto the first confinement layer; and applying asecond confinement layer onto the quantum well structure; the step forremoving the surface-emitting semiconductor layer sequence outside theintended laser region further comprises the steps of: removing the firstconfinement layer and the second confinement layer and the quantum wellstructure; and partially removing the buffer layer outside the intendedlaser region; the step for applying the edge-emitting semiconductorlayer sequence further comprises the steps of; successively applying afirst cladding layer, a first waveguide layer, an active layer, a secondwaveguide layer and a second cladding layer onto an uncovered region ofthe buffer layer, wherein a respective layer thickness is designed suchthat a pump radiation generated in the active layer proceeds into thequantum well structure.
 28. A method for manufacturing an opticallypumped surface-emitting semiconductor laser device comprising: applyingan edge-emitting semiconductor layer sequence onto a substrate; furtherapplying a surface-emitting semiconductor laser layer sequence having aquantum well structure onto the edge-emitting semiconductor layersequence; removing the surface-emitting semiconductor laser layersequence outside an intended laser region; and forming at least onecurrent injection path in the edge-emitting semiconductor layersequence.
 29. A method according to claim 28, further comprising thesteps of: performing said applying step via: applying a buffer layeronto the substrate; successively applying a first waveguide layer, anactive layer and a second waveguide layer onto the buffer layer;performing said further applying step via: applying a first confinementlayer onto the second waveguide layer; applying the quantum wellstructure suited for a surface-emitting semiconductor laser onto thefirst confinement layer; applying a second confinement layer onto thequantum well structure; performing said removing step via: removing thefirst confinement layer and the second confinement layer and the quantumwell structure; and partially removing the second waveguide layeroutside the intended surface-emitting laser region.